/*******************************************************************************
 * Copyright (c) 2009, 2014 IBM Corp.
 * <p/>
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * and Eclipse Distribution License v1.0 which accompany this distribution.
 * <p/>
 * The Eclipse Public License is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 * <p/>
 * Contributors:
 * Dave Locke - initial API and implementation and/or initial documentation
 * Ian Craggs - MQTT 3.1.1 support
 */
package com.app.mingluxing.mqttsource;

import com.app.mingluxing.mqttsource.internal.ClientComms;
import com.app.mingluxing.mqttsource.internal.ConnectActionListener;
import com.app.mingluxing.mqttsource.internal.ExceptionHelper;
import com.app.mingluxing.mqttsource.internal.LocalNetworkModule;
import com.app.mingluxing.mqttsource.internal.NetworkModule;
import com.app.mingluxing.mqttsource.internal.SSLNetworkModule;
import com.app.mingluxing.mqttsource.internal.TCPNetworkModule;
import com.app.mingluxing.mqttsource.internal.security.SSLSocketFactoryFactory;
import com.app.mingluxing.mqttsource.internal.wire.MqttDisconnect;
import com.app.mingluxing.mqttsource.internal.wire.MqttPublish;
import com.app.mingluxing.mqttsource.internal.wire.MqttSubscribe;
import com.app.mingluxing.mqttsource.internal.wire.MqttUnsubscribe;
import com.app.mingluxing.mqttsource.logging.Logger;
import com.app.mingluxing.mqttsource.logging.LoggerFactory;
import com.app.mingluxing.mqttsource.persist.MemoryPersistence;
import com.app.mingluxing.mqttsource.persist.MqttDefaultFilePersistence;
import com.app.mingluxing.mqttsource.util.Debug;

import java.util.Hashtable;
import java.util.Properties;

import javax.net.SocketFactory;
import javax.net.ssl.SSLSocketFactory;


/**
 * Lightweight client for talking to an MQTT server using non-blocking methods
 * that allow an operation to run in the background.
 *
 * <p>This class implements the non-blocking {@link IMqttAsyncClient} client interface
 * allowing applications to initiate MQTT actions and then carry on working while the
 * MQTT action completes on a background thread.
 * This implementation is compatible with all Java SE runtimes from 1.4.2 and up.
 * </p>
 * <p>An application can connect to an MQTT server using:
 * <ul>
 * <li>A plain TCP socket
 * <li>A secure SSL/TLS socket
 * </ul>
 * </p>
 * <p>To enable messages to be delivered even across network and client restarts
 * messages need to be safely stored until the message has been delivered at the requested
 * quality of service. A pluggable persistence mechanism is provided to store the messages.
 * </p>
 * <p>By default {@link MqttDefaultFilePersistence} is used to store messages to a file.
 * If persistence is set to null then messages are stored in memory and hence can be lost
 * if the client, Java runtime or device shuts down.
 * </p>
 * <p>If connecting with {@link MqttConnectOptions#setCleanSession(boolean)} set to true it
 * is safe to use memory persistence as all state is cleared when a client disconnects. If
 * connecting with cleanSession set to false in order to provide reliable message delivery
 * then a persistent message store such as the default one should be used.
 * </p>
 * <p>The message store interface is pluggable. Different stores can be used by implementing
 * the {@link MqttClientPersistence} interface and passing it to the clients constructor.
 * </p>
 *
 * @see IMqttAsyncClient
 */
public class MqttAsyncClient implements IMqttAsyncClient { // DestinationProvider {
    private static final String CLASS_NAME = MqttAsyncClient.class.getName();
    private static final Logger log = LoggerFactory.getLogger(LoggerFactory.MQTT_CLIENT_MSG_CAT, CLASS_NAME);

    private static final String CLIENT_ID_PREFIX = "paho";
    private static final long QUIESCE_TIMEOUT = 30000; // ms
    private static final long DISCONNECT_TIMEOUT = 10000; // ms
    private static final char MIN_HIGH_SURROGATE = '\uD800';
    private static final char MAX_HIGH_SURROGATE = '\uDBFF';
    private String clientId;
    private String serverURI;
    protected ClientComms comms;
    private Hashtable topics;
    private MqttClientPersistence persistence;

    /**
     * Create an MqttAsyncClient that is used to communicate with an MQTT server.
     * <p>
     * The address of a server can be specified on the constructor. Alternatively
     * a list containing one or more servers can be specified using the
     * {@link MqttConnectOptions#setServerURIs(String[]) setServerURIs} method
     * on MqttConnectOptions.
     *
     * <p>The <code>serverURI</code> parameter is typically used with the
     * the <code>clientId</code> parameter to form a key. The key
     * is used to store and reference messages while they are being delivered.
     * Hence the serverURI specified on the constructor must still be specified even if a list
     * of servers is specified on an MqttConnectOptions object.
     * The serverURI on the constructor must remain the same across
     * restarts of the client for delivery of messages to be maintained from a given
     * client to a given server or set of servers.
     *
     * <p>The address of the server to connect to is specified as a URI. Two types of
     * connection are supported <code>tcp://</code> for a TCP connection and
     * <code>ssl://</code> for a TCP connection secured by SSL/TLS.
     * For example:
     * <ul>
     * 	<li><code>tcp://localhost:1883</code></li>
     * 	<li><code>ssl://localhost:8883</code></li>
     * </ul>
     * If the port is not specified, it will
     * default to 1883 for <code>tcp://</code>" URIs, and 8883 for <code>ssl://</code> URIs.
     * </p>
     *
     * <p>
     * A client identifier <code>clientId</code> must be specified and be less that 65535 characters.
     * It must be unique across all clients connecting to the same
     * server. The clientId is used by the server to store data related to the client,
     * hence it is important that the clientId remain the same when connecting to a server
     * if durable subscriptions or reliable messaging are required.
     * <p>A convenience method is provided to generate a random client id that
     * should satisfy this criteria - {@link #generateClientId()}. As the client identifier
     * is used by the server to identify a client when it reconnects, the client must use the
     * same identifier between connections if durable subscriptions or reliable
     * delivery of messages is required.
     * </p>
     * <p>
     * In Java SE, SSL can be configured in one of several ways, which the
     * client will use in the following order:
     * </p>
     * <ul>
     * 	<li><strong>Supplying an <code>SSLSocketFactory</code></strong> - applications can
     * use {@link MqttConnectOptions#setSocketFactory(SocketFactory)} to supply
     * a factory with the appropriate SSL settings.</li>
     * 	<li><strong>SSL Properties</strong> - applications can supply SSL settings as a
     * simple Java Properties using {@link MqttConnectOptions#setSSLProperties(Properties)}.</li>
     * 	<li><strong>Use JVM settings</strong> - There are a number of standard
     * Java system properties that can be used to configure key and trust stores.</li>
     * </ul>
     *
     * <p>In Java ME, the platform settings are used for SSL connections.</p>
     *
     * <p>An instance of the default persistence mechanism {@link MqttDefaultFilePersistence}
     * is used by the client. To specify a different persistence mechanism or to turn
     * off persistence, use the {@link #MqttAsyncClient(String, String, MqttClientPersistence)}
     * constructor.
     *
     * @param serverURI the address of the server to connect to, specified as a URI. Can be overridden using
     * {@link MqttConnectOptions#setServerURIs(String[])}
     * @param clientId a client identifier that is unique on the server being connected to
     * @throws IllegalArgumentException if the URI does not start with
     * "tcp://", "ssl://" or "local://".
     * @throws IllegalArgumentException if the clientId is null or is greater than 65535 characters in length
     * @throws MqttException if any other problem was encountered
     */
    public MqttAsyncClient(String serverURI, String clientId) throws MqttException {
        this(serverURI, clientId, new MqttDefaultFilePersistence());
    }

    public MqttAsyncClient(String serverURI, String clientId, MqttClientPersistence persistence) throws MqttException {
        this(serverURI, clientId, persistence, new TimerPingSender());
    }

    /**
     * Create an MqttAsyncClient that is used to communicate with an MQTT server.
     * <p>
     * The address of a server can be specified on the constructor. Alternatively
     * a list containing one or more servers can be specified using the
     * {@link MqttConnectOptions#setServerURIs(String[]) setServerURIs} method
     * on MqttConnectOptions.
     *
     * <p>The <code>serverURI</code> parameter is typically used with the
     * the <code>clientId</code> parameter to form a key. The key
     * is used to store and reference messages while they are being delivered.
     * Hence the serverURI specified on the constructor must still be specified even if a list
     * of servers is specified on an MqttConnectOptions object.
     * The serverURI on the constructor must remain the same across
     * restarts of the client for delivery of messages to be maintained from a given
     * client to a given server or set of servers.
     *
     * <p>The address of the server to connect to is specified as a URI. Two types of
     * connection are supported <code>tcp://</code> for a TCP connection and
     * <code>ssl://</code> for a TCP connection secured by SSL/TLS.
     * For example:
     * <ul>
     * 	<li><code>tcp://localhost:1883</code></li>
     * 	<li><code>ssl://localhost:8883</code></li>
     * </ul>
     * If the port is not specified, it will
     * default to 1883 for <code>tcp://</code>" URIs, and 8883 for <code>ssl://</code> URIs.
     * </p>
     *
     * <p>
     * A client identifier <code>clientId</code> must be specified and be less that 65535 characters.
     * It must be unique across all clients connecting to the same
     * server. The clientId is used by the server to store data related to the client,
     * hence it is important that the clientId remain the same when connecting to a server
     * if durable subscriptions or reliable messaging are required.
     * <p>A convenience method is provided to generate a random client id that
     * should satisfy this criteria - {@link #generateClientId()}. As the client identifier
     * is used by the server to identify a client when it reconnects, the client must use the
     * same identifier between connections if durable subscriptions or reliable
     * delivery of messages is required.
     * </p>
     * <p>
     * In Java SE, SSL can be configured in one of several ways, which the
     * client will use in the following order:
     * </p>
     * <ul>
     * 	<li><strong>Supplying an <code>SSLSocketFactory</code></strong> - applications can
     * use {@link MqttConnectOptions#setSocketFactory(SocketFactory)} to supply
     * a factory with the appropriate SSL settings.</li>
     * 	<li><strong>SSL Properties</strong> - applications can supply SSL settings as a
     * simple Java Properties using {@link MqttConnectOptions#setSSLProperties(Properties)}.</li>
     * 	<li><strong>Use JVM settings</strong> - There are a number of standard
     * Java system properties that can be used to configure key and trust stores.</li>
     * </ul>
     *
     * <p>In Java ME, the platform settings are used for SSL connections.</p>
     * <p>
     * A persistence mechanism is used to enable reliable messaging.
     * For messages sent at qualities of service (QoS) 1 or 2 to be reliably delivered,
     * messages must be stored (on both the client and server) until the delivery of the message
     * is complete. If messages are not safely stored when being delivered then
     * a failure in the client or server can result in lost messages. A pluggable
     * persistence mechanism is supported via the {@link MqttClientPersistence}
     * interface. An implementer of this interface that safely stores messages
     * must be specified in order for delivery of messages to be reliable. In
     * addition {@link MqttConnectOptions#setCleanSession(boolean)} must be set
     * to false. In the event that only QoS 0 messages are sent or received or
     * cleanSession is set to true then a safe store is not needed.
     * </p>
     * <p>An implementation of file-based persistence is provided in
     * class {@link MqttDefaultFilePersistence} which will work in all Java SE based
     * systems. If no persistence is needed, the persistence parameter
     * can be explicitly set to <code>null</code>.</p>
     *
     * @param serverURI the address of the server to connect to, specified as a URI. Can be overridden using
     * {@link MqttConnectOptions#setServerURIs(String[])}
     * @param clientId a client identifier that is unique on the server being connected to
     * @param persistence the persistence class to use to store in-flight message. If null then the
     * default persistence mechanism is used
     * @throws IllegalArgumentException if the URI does not start with
     * "tcp://", "ssl://" or "local://"
     * @throws IllegalArgumentException if the clientId is null or is greater than 65535 characters in length
     * @throws MqttException if any other problem was encountered
     */
    public MqttAsyncClient(String serverURI, String clientId, MqttClientPersistence persistence, MqttPingSender pingSender) throws MqttException {
        final String methodName = "MqttAsyncClient";

        log.setResourceName(clientId);

        if (clientId == null) { //Support empty client Id, 3.1.1 standard
            throw new IllegalArgumentException("Null clientId");
        }
        // Count characters, surrogate pairs count as one character.
        int clientIdLength = 0;
        for (int i = 0; i < clientId.length() - 1; i++) {
            if (Character_isHighSurrogate(clientId.charAt(i)))
                i++;
            clientIdLength++;
        }
        if (clientIdLength > 65535) {
            throw new IllegalArgumentException("ClientId longer than 65535 characters");
        }

        MqttConnectOptions.validateURI(serverURI);

        this.serverURI = serverURI;
        this.clientId = clientId;

        this.persistence = persistence;
        if (this.persistence == null) {
            this.persistence = new MemoryPersistence();
        }

        // @TRACE 101=<init> ClientID={0} ServerURI={1} PersistenceType={2}
        log.fine(CLASS_NAME, methodName, "101", new Object[]{clientId, serverURI, persistence});

        this.persistence.open(clientId, serverURI);
        this.comms = new ClientComms(this, this.persistence, pingSender);
        this.persistence.close();
        this.topics = new Hashtable();

    }


    /**
     * @param ch
     * @return returns 'true' if the character is a high-surrogate code unit
     */
    protected static boolean Character_isHighSurrogate(char ch) {
        return (ch >= MIN_HIGH_SURROGATE) && (ch <= MAX_HIGH_SURROGATE);
    }

    /**
     * Factory method to create an array of network modules, one for
     * each of the supplied URIs
     *
     * @param address the URI for the server.
     * @return a network module appropriate to the specified address.
     */

    // may need an array of these network modules
    protected NetworkModule[] createNetworkModules(String address, MqttConnectOptions options) throws MqttException, MqttSecurityException {
        final String methodName = "createNetworkModules";
        // @TRACE 116=URI={0}
        log.fine(CLASS_NAME, methodName, "116", new Object[]{address});

        NetworkModule[] networkModules = null;
        String[] serverURIs = options.getServerURIs();
        String[] array = null;
        if (serverURIs == null) {
            array = new String[]{address};
        } else if (serverURIs.length == 0) {
            array = new String[]{address};
        } else {
            array = serverURIs;
        }

        networkModules = new NetworkModule[array.length];
        for (int i = 0; i < array.length; i++) {
            networkModules[i] = createNetworkModule(array[i], options);
        }

        log.fine(CLASS_NAME, methodName, "108");
        return networkModules;
    }

    /**
     * Factory method to create the correct network module, based on the
     * supplied address URI.
     *
     * @param address the URI for the server.
     * @param  options
     * @return a network module appropriate to the specified address.
     */
    private NetworkModule createNetworkModule(String address, MqttConnectOptions options) throws MqttException, MqttSecurityException {
        final String methodName = "createNetworkModule";
        // @TRACE 115=URI={0}
        log.fine(CLASS_NAME, methodName, "115", new Object[]{address});

        NetworkModule netModule;
        String shortAddress;
        String host;
        int port;
        SocketFactory factory = options.getSocketFactory();

        int serverURIType = MqttConnectOptions.validateURI(address);

        switch (serverURIType) {
            case MqttConnectOptions.URI_TYPE_TCP:
                shortAddress = address.substring(6);
                host = getHostName(shortAddress);
                port = getPort(shortAddress, 1883);
                if (factory == null) {
                    factory = SocketFactory.getDefault();
                } else if (factory instanceof SSLSocketFactory) {
                    throw ExceptionHelper.createMqttException(MqttException.REASON_CODE_SOCKET_FACTORY_MISMATCH);
                }
                netModule = new TCPNetworkModule(factory, host, port, clientId);
                ((TCPNetworkModule) netModule).setConnectTimeout(options.getConnectionTimeout());
                break;
            case MqttConnectOptions.URI_TYPE_SSL:
                shortAddress = address.substring(6);
                host = getHostName(shortAddress);
                port = getPort(shortAddress, 8883);
                SSLSocketFactoryFactory factoryFactory = null;
                if (factory == null) {
//				try {
                    factoryFactory = new SSLSocketFactoryFactory();
                    Properties sslClientProps = options.getSSLProperties();
                    if (null != sslClientProps)
                        factoryFactory.initialize(sslClientProps, null);
                    factory = factoryFactory.createSocketFactory(null);
//				}
//				catch (MqttDirectException ex) {
//					throw ExceptionHelper.createMqttException(ex.getCause());
//				}
                } else if ((factory instanceof SSLSocketFactory) == false) {
                    throw ExceptionHelper.createMqttException(MqttException.REASON_CODE_SOCKET_FACTORY_MISMATCH);
                }

                // Create the network module...
                netModule = new SSLNetworkModule((SSLSocketFactory) factory, host, port, clientId);
                ((SSLNetworkModule) netModule).setSSLhandshakeTimeout(options.getConnectionTimeout());
                // Ciphers suites need to be set, if they are available
                if (factoryFactory != null) {
                    String[] enabledCiphers = factoryFactory.getEnabledCipherSuites(null);
                    if (enabledCiphers != null) {
                        ((SSLNetworkModule) netModule).setEnabledCiphers(enabledCiphers);
                    }
                }
                break;
            case MqttConnectOptions.URI_TYPE_LOCAL:
                netModule = new LocalNetworkModule(address.substring(8));
                break;
            default:
                // This shouldn't happen, as long as validateURI() has been called.
                netModule = null;
        }
        return netModule;
    }

    private int getPort(String uri, int defaultPort) {
        int port;
        int portIndex = uri.lastIndexOf(':');
        if (portIndex == -1) {
            port = defaultPort;
        } else {
            port = Integer.parseInt(uri.substring(portIndex + 1));
        }
        return port;
    }

    private String getHostName(String uri) {
        int schemeIndex = uri.lastIndexOf('/');
        int portIndex = uri.lastIndexOf(':');
        if (portIndex == -1) {
            portIndex = uri.length();
        }
        return uri.substring(schemeIndex + 1, portIndex);
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#connect(java.lang.Object, org.eclipse.paho.client.mqttv3.IMqttActionListener)
     */
    public IMqttToken connect(Object userContext, IMqttActionListener callback)
            throws MqttException, MqttSecurityException {
        return this.connect(new MqttConnectOptions(), userContext, callback);
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#connect()
     */
    public IMqttToken connect() throws MqttException, MqttSecurityException {
        return this.connect(null, null);
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#connect(org.eclipse.paho.client.mqttv3.MqttConnectOptions)
     */
    public IMqttToken connect(MqttConnectOptions options) throws MqttException, MqttSecurityException {
        return this.connect(options, null, null);
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#connect(org.eclipse.paho.client.mqttv3.MqttConnectOptions, java.lang.Object, org.eclipse.paho.client.mqttv3.IMqttActionListener)
     */
    public IMqttToken connect(MqttConnectOptions options, Object userContext, IMqttActionListener callback)
            throws MqttException, MqttSecurityException {
        final String methodName = "connect";
        if (comms.isConnected()) {
            throw ExceptionHelper.createMqttException(MqttException.REASON_CODE_CLIENT_CONNECTED);
        }
        if (comms.isConnecting()) {
            throw new MqttException(MqttException.REASON_CODE_CONNECT_IN_PROGRESS);
        }
        if (comms.isDisconnecting()) {
            throw new MqttException(MqttException.REASON_CODE_CLIENT_DISCONNECTING);
        }
        if (comms.isClosed()) {
            throw new MqttException(MqttException.REASON_CODE_CLIENT_CLOSED);
        }

        // @TRACE 103=cleanSession={0} connectionTimeout={1} TimekeepAlive={2} userName={3} password={4} will={5} userContext={6} callback={7}
        log.fine(CLASS_NAME, methodName, "103",
                new Object[]{
                        Boolean.valueOf(options.isCleanSession()),
                        new Integer(options.getConnectionTimeout()),
                        new Integer(options.getKeepAliveInterval()),
                        options.getUserName(),
                        ((null == options.getPassword()) ? "[null]" : "[notnull]"),
                        ((null == options.getWillMessage()) ? "[null]" : "[notnull]"),
                        userContext,
                        callback});
        comms.setNetworkModules(createNetworkModules(serverURI, options));

        // Insert our own callback to iterate through the URIs till the connect succeeds
        MqttToken userToken = new MqttToken(getClientId());
        ConnectActionListener connectActionListener = new ConnectActionListener(this, persistence, comms, options, userToken, userContext, callback);
        userToken.setActionCallback(connectActionListener);
        userToken.setUserContext(this);

        comms.setNetworkModuleIndex(0);
        connectActionListener.connect();

        return userToken;
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#disconnect(java.lang.Object, org.eclipse.paho.client.mqttv3.IMqttActionListener)
     */
    public IMqttToken disconnect(Object userContext, IMqttActionListener callback) throws MqttException {
        return this.disconnect(QUIESCE_TIMEOUT, userContext, callback);
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#disconnect()
     */
    public IMqttToken disconnect() throws MqttException {
        return this.disconnect(null, null);
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#disconnect(long)
     */
    public IMqttToken disconnect(long quiesceTimeout) throws MqttException {
        return this.disconnect(quiesceTimeout, null, null);
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#disconnect(long, java.lang.Object, org.eclipse.paho.client.mqttv3.IMqttActionListener)
     */
    public IMqttToken disconnect(long quiesceTimeout, Object userContext, IMqttActionListener callback) throws MqttException {
        final String methodName = "disconnect";
        // @TRACE 104=> quiesceTimeout={0} userContext={1} callback={2}
        log.fine(CLASS_NAME, methodName, "104", new Object[]{new Long(quiesceTimeout), userContext, callback});

        MqttToken token = new MqttToken(getClientId());
        token.setActionCallback(callback);
        token.setUserContext(userContext);

        MqttDisconnect disconnect = new MqttDisconnect();
        try {
            comms.disconnect(disconnect, quiesceTimeout, token);
        } catch (MqttException ex) {
            //@TRACE 105=< exception
            log.fine(CLASS_NAME, methodName, "105", null, ex);
            throw ex;
        }
        //@TRACE 108=<
        log.fine(CLASS_NAME, methodName, "108");

        return token;
    }

    /*
     * (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#disconnectForcibly()
     */
    public void disconnectForcibly() throws MqttException {
        disconnectForcibly(QUIESCE_TIMEOUT, DISCONNECT_TIMEOUT);
    }

    /*
     * (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#disconnectForcibly(long)
     */
    public void disconnectForcibly(long disconnectTimeout) throws MqttException {
        disconnectForcibly(QUIESCE_TIMEOUT, disconnectTimeout);
    }

    /*
     * (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#disconnectForcibly(long, long)
     */
    public void disconnectForcibly(long quiesceTimeout, long disconnectTimeout) throws MqttException {
        comms.disconnectForcibly(quiesceTimeout, disconnectTimeout);
    }

    /* (non-Javadoc)
     * @see IMqttAsyncClient#isConnected()
     */
    public boolean isConnected() {
        return comms.isConnected();
    }

    /* (non-Javadoc)
     * @see IMqttAsyncClient#getClientId()
     */
    public String getClientId() {
        return clientId;
    }

    /* (non-Javadoc)
     * @see IMqttAsyncClient#getServerURI()
     */
    public String getServerURI() {
        return serverURI;
    }

//	* <li>{@link MqttAsyncClient#publish(String, MqttMessage, MqttDeliveryToken)} to publish a message in a non-blocking manner or
//	* <li>{@link MqttClient#publishBlock(String, MqttMessage, MqttDeliveryToken)} to publish a message in a blocking manner

    /**
     * Get a topic object which can be used to publish messages.
     * <p>There are two alternative methods that should be used in preference to this one when publishing a message:
     * <ul>
     * </ul>
     * </p>
     * <p>When you build an application,
     * the design of the topic tree should take into account the following principles
     * of topic name syntax and semantics:</p>
     *
     * <ul>
     * 	<li>A topic must be at least one character long.</li>
     * 	<li>Topic names are case sensitive.  For example, <em>ACCOUNTS</em> and <em>Accounts</em> are
     * 	two different topics.</li>
     * 	<li>Topic names can include the space character.  For example, <em>Accounts
     * 	payable</em> is a valid topic.</li>
     * 	<li>A leading "/" creates a distinct topic.  For example, <em>/finance</em> is
     * 	different from <em>finance</em>. <em>/finance</em> matches "+/+" and "/+", but
     * 	not "+".</li>
     * 	<li>Do not include the null character (Unicode<samp class="codeph"> \x0000</samp>) in
     * 	any topic.</li>
     * </ul>
     *
     * <p>The following principles apply to the construction and content of a topic
     * tree:</p>
     *
     * <ul>
     * 	<li>The length is limited to 64k but within that there are no limits to the
     * 	number of levels in a topic tree.</li>
     * 	<li>There can be any number of root nodes; that is, there can be any number
     * 	of topic trees.</li>
     * 	</ul>
     * </p>
     *
     * @param topic the topic to use, for example "finance/stock/ibm".
     * @return an MqttTopic object, which can be used to publish messages to
     * the topic.
     * @throws IllegalArgumentException if the topic contains a '+' or '#'
     * wildcard character.
     */
    protected MqttTopic getTopic(String topic) {
        MqttTopic.validate(topic, false/*wildcards NOT allowed*/);

        MqttTopic result = (MqttTopic) topics.get(topic);
        if (result == null) {
            result = new MqttTopic(topic, comms);
            topics.put(topic, result);
        }
        return result;
    }

    /* (non-Javadoc)
     * Check and send a ping if needed.
     * <p>By default, client sends PingReq to server to keep the connection to
     * server. For some platforms which cannot use this mechanism, such as Android,
     * developer needs to handle the ping request manually with this method.
     * </p>
     *
     * @throws MqttException for other errors encountered while publishing the message.
     */
    public IMqttToken checkPing(Object userContext, IMqttActionListener callback) throws MqttException {
        final String methodName = "ping";
        MqttToken token;
        //@TRACE 117=>
        log.fine(CLASS_NAME, methodName, "117");

        token = comms.checkForActivity();
        //@TRACE 118=<
        log.fine(CLASS_NAME, methodName, "118");

        return token;
    }


    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#subscribe(java.lang.String, int, java.lang.Object, org.eclipse.paho.client.mqttv3.IMqttActionListener)
     */
    public IMqttToken subscribe(String topicFilter, int qos, Object userContext, IMqttActionListener callback) throws MqttException {
        return this.subscribe(new String[]{topicFilter}, new int[]{qos}, userContext, callback);
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#subscribe(java.lang.String, int)
     */
    public IMqttToken subscribe(String topicFilter, int qos) throws MqttException {
        return this.subscribe(new String[]{topicFilter}, new int[]{qos}, null, null);
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#subscribe(java.lang.String[], int[])
     */
    public IMqttToken subscribe(String[] topicFilters, int[] qos) throws MqttException {
        return this.subscribe(topicFilters, qos, null, null);
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#subscribe(java.lang.String[], int[], java.lang.Object, org.eclipse.paho.client.mqttv3.IMqttActionListener)
     */
    public IMqttToken subscribe(String[] topicFilters, int[] qos, Object userContext, IMqttActionListener callback) throws MqttException {
        final String methodName = "subscribe";

        if (topicFilters.length != qos.length) {
            throw new IllegalArgumentException();
        }

        String subs = "";
        for (int i = 0; i < topicFilters.length; i++) {
            if (i > 0) {
                subs += ", ";
            }
            subs += "topic=" + topicFilters[i] + " qos=" + qos[i];

            //Check if the topic filter is valid before subscribing
            MqttTopic.validate(topicFilters[i], true/*allow wildcards*/);
        }
        //@TRACE 106=Subscribe topicFilter={0} userContext={1} callback={2}
        log.fine(CLASS_NAME, methodName, "106", new Object[]{subs, userContext, callback});

        MqttToken token = new MqttToken(getClientId());
        token.setActionCallback(callback);
        token.setUserContext(userContext);
        token.internalTok.setTopics(topicFilters);

        MqttSubscribe register = new MqttSubscribe(topicFilters, qos);

        comms.sendNoWait(register, token);
        //@TRACE 109=<
        log.fine(CLASS_NAME, methodName, "109");

        return token;
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#unsubscribe(java.lang.String, java.lang.Object, org.eclipse.paho.client.mqttv3.IMqttActionListener)
     */
    public IMqttToken unsubscribe(String topicFilter, Object userContext, IMqttActionListener callback) throws MqttException {
        return unsubscribe(new String[]{topicFilter}, userContext, callback);
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#unsubscribe(java.lang.String)
     */
    public IMqttToken unsubscribe(String topicFilter) throws MqttException {
        return unsubscribe(new String[]{topicFilter}, null, null);
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#unsubscribe(java.lang.String[])
     */
    public IMqttToken unsubscribe(String[] topicFilters) throws MqttException {
        return unsubscribe(topicFilters, null, null);
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#unsubscribe(java.lang.String[], java.lang.Object, org.eclipse.paho.client.mqttv3.IMqttActionListener)
     */
    public IMqttToken unsubscribe(String[] topicFilters, Object userContext, IMqttActionListener callback) throws MqttException {
        final String methodName = "unsubscribe";
        String subs = "";
        for (int i = 0; i < topicFilters.length; i++) {
            if (i > 0) {
                subs += ", ";
            }
            subs += topicFilters[i];

            // Check if the topic filter is valid before unsubscribing
            // Although we already checked when subscribing, but invalid
            // topic filter is meanless for unsubscribing, just prohibit it
            // to reduce unnecessary control packet send to broker.
            MqttTopic.validate(topicFilters[i], true/*allow wildcards*/);
        }

        //@TRACE 107=Unsubscribe topic={0} userContext={1} callback={2}
        log.fine(CLASS_NAME, methodName, "107", new Object[]{subs, userContext, callback});

        MqttToken token = new MqttToken(getClientId());
        token.setActionCallback(callback);
        token.setUserContext(userContext);
        token.internalTok.setTopics(topicFilters);

        MqttUnsubscribe unregister = new MqttUnsubscribe(topicFilters);

        comms.sendNoWait(unregister, token);
        //@TRACE 110=<
        log.fine(CLASS_NAME, methodName, "110");

        return token;
    }

    /* (non-Javadoc)
     * @see IMqttAsyncClient#setCallback(MqttCallback)
     */
    public void setCallback(MqttCallback callback) {
        comms.setCallback(callback);
    }

    /**
     * Returns a randomly generated client identifier based on the the fixed prefix (paho)
     * and the system time.
     * <p>When cleanSession is set to false, an application must ensure it uses the
     * same client identifier when it reconnects to the server to resume state and maintain
     * assured message delivery.</p>
     * @return a generated client identifier
     * @see MqttConnectOptions#setCleanSession(boolean)
     */
    public static String generateClientId() {
        //length of nanoTime = 15, so total length = 19  < 65535(defined in spec)
        return CLIENT_ID_PREFIX + System.nanoTime();
    }

    /* (non-Javadoc)
     * @see IMqttAsyncClient#getPendingDeliveryTokens()
     */
    public IMqttDeliveryToken[] getPendingDeliveryTokens() {
        return comms.getPendingDeliveryTokens();
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#publish(java.lang.String, byte[], int, boolean, java.lang.Object, org.eclipse.paho.client.mqttv3.IMqttActionListener)
     */
    public IMqttDeliveryToken publish(String topic, byte[] payload, int qos,
                                      boolean retained, Object userContext, IMqttActionListener callback) throws MqttException,
            MqttPersistenceException {
        MqttMessage message = new MqttMessage(payload);
        message.setQos(qos);
        message.setRetained(retained);
        return this.publish(topic, message, userContext, callback);
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#publish(java.lang.String, byte[], int, boolean)
     */
    public IMqttDeliveryToken publish(String topic, byte[] payload, int qos,
                                      boolean retained) throws MqttException, MqttPersistenceException {
        return this.publish(topic, payload, qos, retained, null, null);
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#publish(java.lang.String, org.eclipse.paho.client.mqttv3.MqttMessage)
     */
    public IMqttDeliveryToken publish(String topic, MqttMessage message) throws MqttException, MqttPersistenceException {
        return this.publish(topic, message, null, null);
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#publish(java.lang.String, org.eclipse.paho.client.mqttv3.MqttMessage, java.lang.Object, org.eclipse.paho.client.mqttv3.IMqttActionListener)
     */
    public IMqttDeliveryToken publish(String topic, MqttMessage message, Object userContext, IMqttActionListener callback) throws MqttException,
            MqttPersistenceException {
        final String methodName = "publish";
        //@TRACE 111=< topic={0} message={1}userContext={1} callback={2}
        log.fine(CLASS_NAME, methodName, "111", new Object[]{topic, userContext, callback});

        //Checks if a topic is valid when publishing a message.
        MqttTopic.validate(topic, false/*wildcards NOT allowed*/);

        MqttDeliveryToken token = new MqttDeliveryToken(getClientId());
        token.setActionCallback(callback);
        token.setUserContext(userContext);
        token.setMessage(message);
        token.internalTok.setTopics(new String[]{topic});

        MqttPublish pubMsg = new MqttPublish(topic, message);
        comms.sendNoWait(pubMsg, token);

        //@TRACE 112=<
        log.fine(CLASS_NAME, methodName, "112");

        return token;
    }

    /* (non-Javadoc)
     * @see org.eclipse.paho.client.mqttv3.IMqttAsyncClient#close()
     */
    public void close() throws MqttException {
        final String methodName = "close";
        //@TRACE 113=<
        log.fine(CLASS_NAME, methodName, "113");
        comms.close();
        //@TRACE 114=>
        log.fine(CLASS_NAME, methodName, "114");

    }

    /**
     * Return a debug object that can be used to help solve problems.
     */
    public Debug getDebug() {
        return new Debug(clientId, comms);
    }

}
